Re: PIE for older browsers
As far as I know DD_roundies doesn't do anything special for older browser versions. But it's only doing rounded corners, which have been supported in Safari (to some degree) via -webkit-border-radius since 3.0 and in Mozilla's engine via -moz-border-radius for a decade or so.
PIE does more than just border-radius of course, so not all the properties have as wide support in older browsers. Background gradients are a big one for example, not supported in FF until 3.6.
While it would be possible to write a similar tool to add support in old non-IE browsers, PIE probably isn't the right place. First of all, it's implemented as an htc behavior which is only supported in IE. You'd probably want an XBL version for Mozilla... Safari would require a straight JS file which would have implications in terms of performance and the work required to handle automatic attachment/detachment. If someone wanted to take this on they could probably reuse some of PIE's parsing code, but the rest would be pretty different.
Personally, given the relatively fast uptake of new browser versions among non-IE users, it seems like an awful lot of work for a quickly vanishing minority. That's just me though, if anyone else wants to take this on by all means have at it!